An ultrasonic flaw detection test is an inspection technology that can nondestructively inspect soundness of a surface and interior of a structural material or the like to be used as a product, and the ultrasonic flaw detection test is used in various fields.
A phased array-type ultrasonic flaw detection test is performed in such a manner that an array probe constituted by arraying plural compact piezoelectric elements for transmitting and receiving ultrasonic waves is directly or indirectly brought into contact with an inspection object. By driving the plural arrayed piezoelectric elements at different timings, ultrasonic waves can be internally transmitted from the array probe to the inspection object at an arbitrary angle.
For this reason, the phased array method can detect flaws in a wide range and multiple angles while fixing the array probe, as compared with the monocular probe method in which ultrasonic waves can be transmitted only at a predetermined angle. Thus, the phased array method for the ultrasonic flaw detection test is possible to target a structural material having a complicated shape and to reduce the number of working steps.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2011-002360
For instance, when ultrasonic flaw detection is performed on an inspection object having coarsened crystal grain and/or anisotropy such as a welded portion, the frequency of an ultrasonic wave transmitted to the inside of the inspection object is sometimes set to a small frequency in order to reduce the influence of noise. In the case of transmitting a low-frequency ultrasonic wave to the inside of the inspection object by the phased array method, it is required to increase the size of each piezoelectric element constituting the array probe in order to secure the detection sensitivity of a flaw.
As one of the driving methods of the piezoelectric elements in the phased array method, there is known a linear scan method. In the linear scan method, the position of the beam line of the ultrasonic beam (i.e., the reference position or the incident position on the inspection object) is moved along the surface of the inspection object while the flaw detection direction (i.e., the direction of the ultrasonic beam, such as the refraction angle, transmitted to the inside of the inspection object) is being kept constant. In the case of executing this linear scanning method, the array pitch of the piezoelectric elements becomes large when the size of each piezoelectric element is increased. As a result, the interval of the ultrasonic beams discretely arranged according to the size of each piezoelectric element is expanded, and there is a problem that the spatial resolution of flaw detection is reduced.
When the size of each piezoelectric element is reduced in order to solve the above-described problem, it is necessary to simultaneously drive plural piezoelectric elements for securing detection sensitivity, which further leads to another problem that the control channels of the piezoelectric elements become enormous.
In view of the above-described problems, an object of embodiments of the present invention is to provide an ultrasonic flaw detection technique with improved spatial resolution of flaw detection and to provide a manufacturing method of a product based on this ultrasonic flaw detection technique.